JP5022696B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention relates to a magnetic resonance imaging apparatus, and transmits an RF pulse to a subject in a static magnetic field space and a magnetic resonance signal generated by transmitting a gradient pulse to the subject to which the RF pulse is transmitted as imaging data. The present invention relates to a magnetic resonance imaging apparatus that performs an obtained imaging sequence and generates an image of a subject based on imaging data obtained by performing the imaging sequence.

  2. Description of the Related Art Magnetic resonance imaging (MRI) apparatuses are often used particularly in medical applications as apparatuses that take an image of a tomographic plane of a subject by using a nuclear magnetic resonance (NMR) phenomenon. ing.

  In a magnetic resonance imaging apparatus, by accommodating a subject in an imaging space in which a static magnetic field is formed, proton spins in the subject are aligned in the direction of the static magnetic field, and a magnetization vector is obtained. generate. Then, the spin is flipped by irradiating an RF pulse having a resonance frequency to cause a nuclear magnetic resonance phenomenon to change the proton magnetization vector, and then the spin is moved along the direction of the static magnetic field. A scan for receiving a magnetic resonance (MR) signal generated when returning to the state of the magnetization vector is performed as an imaging sequence. Then, an image such as a slice image is generated for the subject using the magnetic resonance signal obtained by the execution of the imaging sequence as imaging data.

  In this magnetic resonance imaging apparatus, angiography called MRA (MR angiography) is performed in order to depict a flow such as blood flowing through a blood vessel. In MRA, there is an imaging method using a time of flight (TOF) effect or a phase contrast (PC) effect. As an imaging method that does not use a contrast agent, FBI (Fresh Blood Imaging) has been proposed (see, for example, Patent Document 1 and Patent Document 2).

JP 2000-5144 A Japanese Patent Laid-Open No. 2002-200054

  In the FBI method, an imaging sequence is performed in each of diastole and systole to generate an image of a subject. Then, based on the difference value between these images, an MRA image relating to the subject is obtained. In this method, a flow void of FSE (Fast Spin Echo) method is applied.

  Specifically, first, a first image is generated by performing an imaging sequence in a diastole. For example, without transmitting a gradient pulse for flow compensation in the read direction and without transmitting a crusher gradient pulse in the warp direction, the slice A scan is performed by transmitting a crusher gradient pulse in the direction to generate a first image.

  Then, a second image is generated by performing an imaging sequence in the systole period. For example, in the read direction, the warp direction, and the slice direction, scanning is performed by transmitting a crusher gradient pulse before transmitting a read gradient pulse that reads a magnetic resonance signal. Thereby, a flow void is produced in each axial direction, and the second image is generated.

  Thereafter, an MRA image relating to the subject is obtained based on the difference value between the first image and the second image. Here, during the systole, the arterial blood flow rate is fast, so the signal strength from the artery is low, and during diastole, the arterial blood flow rate is slow, so the signal strength from the artery is high, The MRA image generated based on the difference value as described above has high contrast. Specifically, only the portion where the flow void is generated in the second image is drawn.

  However, in the above method, since it is difficult to predict the degree of occurrence of flow voids, MRA images may not be generated with sufficiently high contrast, and it is difficult to obtain appropriate image quality. It was.

  In the above method, the flow may not be drawn properly for the flow in the direction in which the combination of the lead direction and the warp direction is zero, and thus the flow may not be drawn properly. In some cases, it is difficult to generate an MRA image.

  In the above method, since the MRA image is generated based on the difference value between the first image and the second image, the signal intensity becomes lower than the first image, and the noise is increased by √2. Become. For this reason, since the S / N ratio of the MRA image is 1 / √2 or less with respect to the first image, it may be difficult to obtain sufficient image quality.

  Further, in the above method, since the collection of magnetic resonance signals is limited to the FSE method, the versatility may not be sufficient.

  For this reason, in the above method, since the versatility is poor and the image quality may be deteriorated, it may be difficult to improve the diagnostic efficiency.

  Accordingly, an object of the present invention is to provide a magnetic resonance imaging apparatus that is highly versatile and can improve image quality.

  To achieve the above object, the magnetic resonance imaging apparatus of the present invention performs an imaging sequence for obtaining magnetic resonance signals generated from spins excited by a subject in a static magnetic field space as imaging data. A magnetic resonance imaging apparatus for generating an image of the subject based on the imaging data obtained by the step, wherein the magnetic resonance is performed according to a speed of a spin moving in the subject while performing the imaging sequence A scanning unit that performs a preparation sequence for transmitting a preparation pulse to the subject so that the signal intensity of the signal is different before performing the imaging sequence, and the scan unit includes a first RF pulse as the preparation pulse, A pair of gradient pulses is transmitted so that each of the 2RF pulse, the 3rd RF pulse, and the 4th RF pulse is sequentially transmitted to the subject, and the time point when the RF pulse is transmitted as the second RF pulse is sandwiched in the time axis. The second crusher gradient pulse consisting of a pair of gradient pulses is transmitted so that the time point of transmitting the RF pulse as the third RF pulse is sandwiched in the time axis. After transmitting to the sample and transmitting the fourth RF pulse, a killer gradient pulse is transmitted to the subject.

  Preferably, the scanning unit transmits the first RF pulse and the fourth RF pulse so that the phases thereof are the same, the absolute values of the flip angles are the same, and the signs are reversed. To do.

  Preferably, the scanning unit transmits the first RF pulse and the fourth RF pulse so that the absolute value of the flip angle is 90 °.

  Preferably, the scanning unit transmits each of the second RF pulse and the third RF pulse so that the phases thereof are orthogonal to the phases of the first RF pulse and the fourth RF pulse.

  Preferably, the scanning unit transmits the second RF pulse and the third RF pulse so that the absolute values of the flip angles are the same.

  Preferably, the scanning unit applies the second RF pulse with respect to a first time interval between a central time point for transmitting the first RF pulse and a central time point for transmitting the second RF pulse. The second time interval between the central point in time for transmitting and the central point in time for transmitting the third RF pulse is doubled, and the central point in time for transmitting the third RF pulse and the fourth RF pulse are Each of the first RF pulse, the second RF pulse, the third RF pulse, and the fourth RF pulse is sequentially performed so that the third time interval with the central time point of the transmission time is the same. To the subject.

  Preferably, the scanning unit transmits a plurality of RF pulses including a 180 ° pulse as the second RF pulse, and transmits a plurality of RF pulses including the 180 ° pulse as the third RF pulse.

  Preferably, the scan unit transmits the plurality of RF pulses transmitted as the second RF pulse and the third RF pulse, respectively, in the same phase and in the same absolute value of the flip angle. Yes, so that the sign is reversed.

  Preferably, the scanning unit sequentially transmits an α ° pulse other than the 180 ° pulse and a 180 ° pulse as the plurality of RF pulses to be transmitted in each of the second RF pulse and the third RF pulse. .

  Preferably, the scanning unit includes a plurality of gradient pulses transmitted as the first crusher gradient pulse and the second crusher gradient pulse, respectively, between the first RF pulse and the second RF pulse. Each of the gradient pulse to be transmitted and the gradient pulse to be transmitted between the third RF pulse and the fourth RF pulse has the same first time integration value, and the second RF pulse and the third RF pulse So that the total time integral value of the gradient pulses transmitted between the plurality of RF pulses transmitted as each of the first time integral value is doubled with respect to the first time integral value, Each of the first crusher gradient pulse and the second crusher gradient pulse is transmitted.

  Preferably, the scan unit transmits, as the preparation pulse, a velocity encode gradient pulse that shifts the spin phase so that the phase of the spin varies depending on the spin velocity moving in the spin of the subject.

  Preferably, the scan unit transmits the velocity encode gradient pulse so as to have opposite polarities in the time axis with respect to a central time point at which the velocity encode gradient pulse is transmitted.

  Preferably, the image processing unit includes an image generation unit that generates an image of the subject based on the imaging data, and the scan unit performs the imaging sequence after performing the preparation sequence as a first preparation pulse sequence. The magnetic resonance signal generated by this is acquired as first imaging data, and the crusher gradient pulse and the velocity encode gradient pulse are not transmitted, and the flip angles of the second RF pulse and the third RF pulse are different from each other. The imaging sequence is executed after the second preparation pulse sequence that transmits the same preparation pulse as the first preparation sequence is used as the preparation sequence. The magnetic resonance signal generated by the acquisition is acquired as second imaging data, and the image generation unit generates a first image based on the first imaging data, and generates a second image based on the second imaging data. After the image is generated, a difference image is generated as the image by performing a difference process on the first image and the second image.

  Preferably, the scanning unit transmits a killer gradient pulse that generates a gradient magnetic field that causes the transverse magnetization of the spin to disappear in the subject before transmitting the first RF pulse as the preparation pulse.

  Preferably, the scanning unit transmits each of the first RF pulse, the second RF pulse, the third RF pulse, and the fourth RF pulse as a rectangular pulse.

  Preferably, the scanning unit performs the preparation sequence during systole in the heartbeat motion of the subject, and performs the imaging sequence during diastole in the heartbeat motion.

  According to the present invention, it is possible to provide a magnetic resonance imaging apparatus that is highly versatile and can improve image quality.

<Embodiment 1>
A first embodiment according to the present invention will be described.

(Device configuration)
FIG. 1 is a configuration diagram illustrating a configuration of a magnetic resonance imaging apparatus 1 according to the first embodiment of the present invention.

  As shown in FIG. 1, the magnetic resonance imaging apparatus 1 of the present embodiment includes a scanning unit 2 and an operation console unit 3 and is excited by a subject in an imaging space in which a static magnetic field is formed. An imaging sequence for obtaining magnetic resonance signals generated from the spin as imaging data is performed, and an image of the subject is generated based on the imaging data obtained by performing the imaging sequence.

  The present embodiment includes spins of a first spin in a stationary state at a first velocity of 0 and a second spin in a moving state moving at a second velocity different from the first velocity. A subject is accommodated in an imaging space B in which a static magnetic field is formed, and an RF pulse is transmitted to the subject accommodated in the imaging space B to excite the spin and to generate from the excited spin. An imaging sequence for obtaining a magnetic resonance signal as imaging data is performed. Thereafter, an image of the subject is generated based on the imaging data obtained by performing the imaging sequence.

  The scanning unit 2 will be described.

  As shown in FIG. 1, the scanning unit 2 includes a static magnetic field magnet unit 12, a gradient coil unit 13, an RF coil unit 14, a cradle 15, an RF drive unit 22, a gradient drive unit 23, and a data collection unit. 24. As described above, the scanning unit 2 transmits the RF pulse to the subject SU so as to excite the spin of the subject SU in the imaging space B where the static magnetic field is formed, and the RF pulse is transmitted. An imaging sequence IS for obtaining magnetic resonance signals generated in the subject SU as imaging data by transmitting gradient pulses to the subject SU is performed. The scan unit 2 performs the imaging sequence IS, and before the imaging sequence IS is performed, the scanning unit 2 applies the preparation pulse so that the signal intensity of the magnetic resonance signal varies depending on the speed of the spin moving in the subject. The preparation sequence PS to be transmitted to is executed. Specifically, for example, the preparation pulse is set so that the signal intensity of the magnetic resonance signal generated from the first spin in the stationary state and the magnetic resonance signal generated from the second spin in the moving state are different from each other. A preparation sequence to be transmitted to the subject is performed before the imaging sequence is performed.

  Although details will be described later, the scanning unit 2 sequentially supplies each of the first RF pulse, the second RF pulse, the third RF pulse, and the fourth RF pulse to the subject as the preparation pulses in the preparation sequence PS. Send. Along with this, a crusher gradient pulse is transmitted to the subject so that the time point at which each of the second RF pulse and the third RF pulse is transmitted is sandwiched in the time axis. Here, the first crusher gradient pulse composed of a pair of gradient pulses is transmitted to the subject so that the time point at which the RF pulse is transmitted as the second RF pulse is sandwiched in the time axis, and the RF pulse is transmitted as the third RF pulse. A second crusher gradient pulse composed of a pair of gradient pulses is transmitted to the subject so as to sandwich the time point on the time axis. Then, after transmitting the fourth RF pulse and transmitting the crusher gradient pulse, the killer gradient pulse is transmitted to the subject.

  After that, the scanning unit 2 executes the imaging sequence IS by an SSFP (Steady State Free Prescription) type imaging method called FIESTA, True FISP, Balanced TFE, or the like.

  Each component of the scanning unit 2 will be described sequentially.

  The static magnetic field magnet unit 12 is, for example, a horizontal magnetic field type, and is a superconducting magnet so as to be along the body axis direction (z direction) of the subject SU placed in the imaging space B in which the subject SU is accommodated. (Not shown) forms a static magnetic field. The static magnetic field magnet unit 12 may be a vertical magnetic field type in addition to a horizontal magnetic field type, and may form a static magnetic field along a direction in which a pair of permanent magnets face each other.

  The gradient coil unit 13 forms a gradient magnetic field in the imaging space B in which a static magnetic field is formed, and adds spatial position information to the magnetic resonance signal received by the RF coil unit 14. Here, the gradient coil unit 13 includes three systems so as to correspond to three axial directions orthogonal to each other in the z direction along the static magnetic field direction, the x direction, and the y direction. These form a gradient magnetic field by transmitting gradient pulses as a frequency encode direction, a phase encode direction, and a slice selection direction, respectively, according to the set imaging conditions. Specifically, the gradient coil unit 13 applies a gradient magnetic field in the slice selection direction of the subject SU, and selects a slice of the subject SU to be excited when the RF coil unit 14 transmits an RF pulse. The gradient coil unit 13 applies a gradient magnetic field in the phase encoding direction of the subject SU, and phase encodes the magnetic resonance signal from the slice excited by the RF pulse. The gradient coil unit 13 applies a gradient magnetic field in the frequency encoding direction of the subject SU, and frequency encodes the magnetic resonance signal from the slice excited by the RF pulse.

  As shown in FIG. 1, the RF coil unit 14 is disposed so as to surround the subject SU. In the imaging space B where the static magnetic field is formed by the static magnetic field magnet unit 12, the RF coil unit 14 transmits an RF pulse, which is an electromagnetic wave, to the subject SU to form a high-frequency magnetic field, and in the imaging region of the subject SU. Excites proton spin. The RF coil unit 14 receives an electromagnetic wave generated from the excited proton in the subject SU as a magnetic resonance signal.

  The cradle 15 has a table on which the subject SU is placed. The cradle unit 26 moves between the inside and the outside of the imaging space B based on a control signal from the control unit 30.

  The RF drive unit 22 drives the RF coil unit 14 to transmit RF pulses in the imaging space B to form a high-frequency magnetic field. Based on the control signal from the control unit 30, the RF drive unit 22 modulates the signal from the RF oscillator to a signal having a predetermined timing and a predetermined envelope using a gate modulator, and then modulates the signal by the gate modulator. The signal thus amplified is amplified by an RF power amplifier and output to the RF coil unit 14 to transmit an RF pulse.

  Based on a control signal from the control unit 30, the gradient driving unit 23 applies a gradient pulse to the gradient coil unit 13 to drive the gradient coil unit 13, thereby generating a gradient magnetic field in the imaging space B in which a static magnetic field is formed. The gradient drive unit 23 includes three systems of drive circuits (not shown) corresponding to the three systems of gradient coil units 13.

  The data collection unit 24 collects magnetic resonance signals received by the RF coil unit 14 based on the control signal from the control unit 30. Here, in the data collecting unit 24, the phase detector detects the magnetic resonance signal received by the RF coil unit 14 using the output of the RF oscillator of the RF driving unit 22 as a reference signal. Thereafter, the magnetic resonance signal, which is an analog signal, is converted into a digital signal using an A / D converter and output.

  The operation console unit 3 will be described.

  As illustrated in FIG. 1, the operation console unit 3 includes a control unit 30, an image generation unit 31, an operation unit 32, a display unit 33, and a storage unit 34.

  Each component of the operation console unit 3 will be described sequentially.

  The control unit 30 includes a computer and a memory that stores a program that causes the computer to execute predetermined data processing, and controls each unit. Here, the control unit 30 receives operation data from the operation unit 32, and each of the RF drive unit 22, the gradient drive unit 23, and the data collection unit 24 based on the operation data input from the operation unit 32. A control signal is output to a predetermined scan. At the same time, a control signal is output to the image generation unit 31, the display unit 33, and the storage unit 34 to perform control.

  The image generation unit 31 includes a computer and a memory that stores a program for executing predetermined data processing using the computer, and executes data processing based on a control signal from the control unit 30. , Generate an image. Here, the image generation unit 31 uses the magnetic resonance signal obtained by the scan unit 2 performing a scan as raw data, and reconstructs an image of the subject SU. Then, the image generation unit 31 outputs the generated image to the display unit 33.

  The operation unit 32 is configured by operation devices such as a keyboard and a pointing device. The operation unit 32 is input with operation data by an operator and outputs the operation data to the control unit 30.

  The display unit 33 is configured by a display device such as a CRT, and displays an image on the display screen based on a control signal from the control unit 30. For example, the display unit 33 displays a plurality of images of input items for which operation data is input to the operation unit 32 by the operator on the display screen. In addition, the display unit 33 receives data about the image of the subject SU generated based on the magnetic resonance signal from the subject SU from the image generation unit 31 and displays the image on the display screen.

  The storage unit 34 includes a memory and stores various data. The storage unit 34 is accessed by the control unit 30 as necessary for the stored data.

(Operation)
Hereinafter, the operation when imaging the subject SU using the magnetic resonance imaging apparatus 1 according to the embodiment of the present invention will be described.

  FIG. 2 is a flowchart showing an operation when imaging the subject SU in the first embodiment according to the present invention.

  First, as shown in FIG. 2, the preparation sequence PS is performed (S11).

  Here, the scanning unit 2 performs the preparation sequence PS.

  FIG. 3 is a pulse sequence diagram showing the preparation sequence PS in the first embodiment according to the present invention.

  In FIG. 3, (a) is a time axis for transmitting the RF pulse RF, (b) is a time axis for transmitting the crusher gradient pulse Gcrush as a gradient pulse, and (c) is as a gradient pulse. The time axis which transmits the killer gradient pulse Gkill is shown, and the horizontal axis indicates time t and the vertical axis indicates the pulse intensity. Here, each of Gcrush and Gkill is at least one axial direction of the slice selection direction, the phase encoding direction, and the frequency encoding direction. In the following, the time integral value is an integral value defined by the pulse intensity and time t.

  As shown in FIG. 3A, FIG. 3B, and FIG. 3C, when the preparation sequence PS is executed, the first RF pulse RF1, the second RF pulse RF2, and the third RF are used as the preparation pulses. The scanning unit 2 transmits the pulse RF3, the fourth RF pulse RF4, the first crusher gradient pulse Gc1, the second crusher gradient pulse Gc2, and the killer pulse Gk to the subject SU.

  In the preparation pulse in this preparation sequence PS, each of the first RF pulse RF1, the second RF pulse RF2, the third RF pulse RF3, and the fourth RF pulse RF4 is a rectangular pulse as shown in FIG. And sequentially transmit to the subject. That is, the spins of the subject are flipped sequentially with respect to each of the four RF pulses of the first RF pulse RF1, the second RF pulse RF2, the third RF pulse RF3, and the fourth RF pulse RF4 at time intervals. To the subject.

  Here, as shown in FIG. 3A, the first RF pulse RF1 and the fourth RF pulse RF4 have the same phase, the same absolute value of the flip angle, and the opposite signs. So that the scanning unit 2 transmits. For example, as shown in FIG. 3A, the first RF pulse RF1 and the fourth RF pulse RF4 have the same phase in the same x direction and the same absolute value of the mutual flip angle of 90 °. The scanning unit 2 transmits so that the sign is reversed. That is, the first RF pulse RF1 is transmitted as a 90 ° x pulse, and the fourth RF pulse RF4 is transmitted as a −90 ° x pulse.

  Specifically, the first RF pulse is set so that the spin of the subject flips at a flip angle of 90 ° along the yz plane including the z direction in which the static magnetic field is formed and the y direction orthogonal to the z direction. RF1 is transmitted. That is, the spin of the subject is rotated by 90 ° about the x direction as the central axis. Then, the spin of the subject is 90 °, which is the same absolute value as the first flip angle, and the spin is flipped along the yz plane in a direction opposite to the direction flipped by transmission of the first RF pulse RF1. Thus, the fourth RF pulse RF4 is transmitted at a flip angle of −90 °. That is, the spin of the subject is rotated by −90 ° with the x direction as the central axis.

  Further, as shown in FIG. 3A, the phase of each of the second RF pulse RF2 and the third RF pulse RF3 is orthogonal to the phases of the first RF pulse RF1 and the fourth RF pulse RF4. Then, the scanning unit 2 transmits. Here, the second RF pulse RF2 and the third RF pulse RF3 are transmitted so that the absolute values of the flip angles are the same. For example, as shown in FIG. 3 (a), each of the second RF pulse RF2 and the third RF pulse RF3 is in the y direction whose phase is orthogonal to the phases of the first RF pulse RF1 and the fourth RF pulse RF4. Then, the scanning unit 2 transmits so that the absolute value of the flip angle is 90 °. That is, the second RF pulse RF2 is transmitted as a 90 ° y pulse, and the third RF pulse RF3 is transmitted as a 90 ° y pulse.

  Specifically, the spin is flipped at a flip angle of 90 ° along the z direction in which the static magnetic field is formed and the xz plane along the x direction orthogonal to the z direction and the y direction. 2RF pulse RF2 is transmitted. That is, the spin of the subject is rotated by 90 ° with the y direction as the central axis. At the same time, the third RF pulse RF3 is transmitted along the xz plane so that the spin is flipped at a flip angle of 90 °. That is, the spin of the subject is rotated by 90 ° with the y direction as the central axis.

  Further, as shown in FIG. 3A, a first time between a central time point tr1 at times t11 to t12 for transmitting the first RF pulse RF1 and a central time point tr2 at times t13 to t14 for transmitting the second RF pulse RF2. With respect to the time interval τ1, the second time interval τ2 between the central time point tr2 of the time t13 to t14 for transmitting the second RF pulse RF2 and the central time point tr3 of the time t15 to t16 for transmitting the third RF pulse RF3 is 2 And the third time interval τ3 between the central time tr3 of the time t15 to t16 for transmitting the third RF pulse RF3 and the central time tr4 of the time t17 to t18 for transmitting the fourth RF pulse RF4 is The first RF pulse RF1, the second RF pulse RF2, the third RF pulse RF3, and the fourth RF pulse R are set to be the same as the first time interval τ1. Each of 4 sequentially transmits to the subject.

  As shown in FIG. 3B, in the preparation pulse in the preparation sequence PS, the first crusher gradient pulse Gc1 and the second crusher gradient pulse Gc2 are the second RF pulse RF2 and the third RF pulse RF3. Are transmitted to the subject as a pair of gradient pulses Gc1a, Gc1b, Gc2a, and Gc2b so that the time points tr2 and tr3 are transmitted on the time axis t.

  Here, among the plurality of gradient pulses Gc1a, Gc1b, Gc2a, and Gc2b transmitted as the first crusher gradient pulse Gc1 and the second crusher gradient pulse Gc2, respectively, between the first RF pulse RF1 and the second RF pulse RF2. Each of the gradient pulse Gc1a to be transmitted to and the gradient pulse Gc2b to be transmitted between the third RF pulse RF3 and the fourth RF pulse RF4 are set to the same first time integration value D1. Along with this, gradient pulses Gc1b and Gc2a transmitted between the plurality of RF pulses transmitted as the second RF pulse RF2 and the third RF pulse RF3 are doubled with respect to the first time integrated value D1. The second time integration value D2 is as follows.

  That is, as shown in FIG. 3B, the time integration value of the gradient pulse Gc1a is D1a, the time integration value of the gradient pulse Gc1b is D1b, the time integration value of the gradient pulse Gc2a is D2a, and the time integration value of the gradient pulse Gc2b is In the case of D2b, the gradient pulses Gc1a, Gc1b, Gc2a, and Gc2b are transmitted as the first crusher gradient pulse Gc1 and the second crusher gradient pulse Gc2 so that the following formula (1) is satisfied.

  2 * D1a = D1b + D2a = 2 * D2b (1)

  In the present embodiment, the gradient pulses Gc1a, Gc1b, Gc2a, and Gc2b are transmitted so that their time integration values are the same. That is, the time integration values of the pair of gradient pulses Gc1a and Gc1b constituting the first crusher gradient pulse Gc1 and the pair of gradient pulses Gc2a and Gc2b constituting the second crusher gradient pulse Gc2 are the same. However, it transmits so that it may become the same polarity. That is, D1a, D1b, D2a, and D2b are all made the same.

  Further, as shown in FIG. 3B, each of the pair of gradient pulses Gc1a and Gc1b constituting the first crusher gradient pulse Gc1 is centered on the central time point tr2 of the time t13 to t14 at which the second RF pulse RF2 is transmitted. Each of the pair of gradient pulses Gc1a and Gc1b is transmitted so as to be symmetrically arranged on the time axis t. Of the pair of gradient pulses Gc1a and Gc1b constituting the first crusher gradient pulse Gc1, the time t1a at which the central time point t1a of transmitting the gradient pulse Gc1a to be transmitted first transmits the first RF pulse RF1. The transmission is performed so as to correspond to the central time point of the first time interval τ1 between the central time point tr1 of t11 to t12 and the central time point tr2 of the time t13 to t14 for transmitting the second RF pulse RF2.

  Further, as shown in FIG. 3B, each of the pair of gradient pulses Gc2a and Gc2b constituting the second crusher gradient pulse Gc2 is centered on the central time point tr3 of the time t15 to t16 at which the third RF pulse RF3 is transmitted. Each of the pair of gradient pulses Gc2a and Gc2b is transmitted so as to be symmetrically arranged on the time axis t. Of the pair of gradient pulses Gc2a and Gc2b constituting the second crusher gradient pulse Gc2, the central time point t2b of the time t16 to t17 for transmitting the gradient pulse Gc2b to be transmitted later is the time t15 for transmitting the third RF pulse RF3. The transmission is performed so as to correspond to the central time point of the third time interval τ3 between the central time point tr3 of ˜t16 and the central time point tr4 of the time t17 to t18 at which the fourth RF pulse RF4 is transmitted.

  In the present embodiment, the transmission state of the first RF pulse RF1, the second RF pulse RF2, and the third RF pulse RF3 is a movement state with respect to the phase of the first spin echo signal SE21 generated from the first spin that is in a stationary state. The phase of the second spin echo signal SE22 generated from the second spin is shifted from the first spin that is stationary by the transmission of the first RF pulse RF1, the second RF pulse RF2, and the third RF pulse RF3. As shown in FIG. 3, the phase of the second stimulated echo signal STE2 generated from the second spin in the moving state is shifted with respect to the phase of the first stimulated echo signal STE1 generated. A first crusher gradient pulse Gc1 composed of a pair of gradient pulses Gc1a and Gc1b is applied to the second RF pulse. A center for transmitting the RF signal RF2 to the subject so as to sandwich the center time tr2 on the time axis t, and transmitting a second crusher gradient pulse Gc2 composed of a pair of gradient pulses Gc2a and Gc2b to the third RF pulse RF3. The time tr3 is transmitted to the subject so as to be sandwiched on the time axis.

  Here, as shown in FIG. 3, the first time interval between the central time point tr1 of the time t11 to t12 for transmitting the first RF pulse RF1 and the central time point tr2 of the time t13 to t14 for transmitting the second RF pulse RF2. At the time tv when the time interval (τ1 * 2) that is twice τ1 has elapsed from the central time tr1 of the time t11 to t12 at which the first RF pulse RF1 is transmitted, the first RF pulse RF1 and the second RF pulse RF2 are transmitted. A spin echo signal SE1 is generated.

  Thereafter, since the spin echo signal SE1 is refocused by the third RF pulse RF3, the central time point tr1 of the time t11 to t12 for transmitting the first RF pulse RF1 and the central time point of the time t13 to t14 for transmitting the second RF pulse RF2. At a time tr4 when a time interval (τ1 * 4) four times the first time interval τ1 with tr2 has elapsed from the central time tr1 of the time t11 to t12 at which the first RF pulse RF1 is transmitted, another spin An echo signal SE2 is generated. That is, the spin echo signal SE2 is generated at the central time point tr4 of the time t17 to t18 at which the fourth RF pulse RF4 is transmitted.

  At this time, the spin echo signal SE22 generated from the second spin in the moving state constitutes the pair of gradient pulses Gc1a and Gc1b constituting the first crusher gradient pulse Gc1 and the second crusher gradient pulse Gc2. The phase is shifted to each of the pair of gradient pulses Gc2a and Gc2b, but the phase of the spin echo signal SE21 generated from the first spin that is in a stationary state is not shifted. Therefore, the phase of the spin echo signal SE22 generated from the second spin in the moving state is shifted from the phase of the spin echo signal SE21 generated from the first spin in the stationary state. Therefore, the spin echo signal SE2 has a phase because the phase is shifted according to the moving speed of the second spin in the moving state.

  On the other hand, at the time tr4 when the spin echo signal SE2 is generated, the stimulated echo signal STE is generated by the transmission of the first RF pulse RF1, the second RF pulse RF2, and the third RF pulse RF3.

  At this time, the stimulated echo signal STE2 generated from the second spin that is in the moving state includes the gradient pulse Gc1a previously transmitted in the pair of gradient pulses Gc1a and Gc1b constituting the first crusher gradient pulse Gc1, and the first The phase of the pair of gradient pulses Gc2a and Gc2b constituting the second crusher gradient pulse Gc2 is shifted by the gradient pulse Gc2b transmitted later, but the stimulated echo signal STE1 generated from the first spin in the stationary state is The phase is not shifted. For this reason, the phase of the stimulated echo signal STE2 generated from the second spin in the moving state is shifted from the phase of the stimulated echo signal STE1 generated from the first spin in the stationary state. . Therefore, the stimulated echo signal STE has a phase because the phase is shifted according to the moving speed of the second spin in the moving state.

  Then, as shown in FIG. 3C, after transmitting the fourth RF pulse RF4, as described above, the crusher gradient pulses Gc1 and Gc2 including the pair of gradient pulses Gc1a, Gc1b, Gc2a, and Gc2b are transmitted. After that, a killer gradient pulse Gk is transmitted to the subject. That is, the gradient that causes the transverse magnetization of the spin to disappear after the second crusher gradient pulse Gc2 is transmitted and between the time t18 after the fourth RF pulse RF4 is transmitted and the time t19 after a predetermined time has elapsed. A killer gradient pulse Gk is transmitted to the subject so that a magnetic field is generated.

  FIG. 4 is a graph showing a simulation result of the relationship between the signal intensity obtained at time t19 after execution of the preparation sequence PS and the speed of the spin moving within the subject in the first embodiment according to the present invention. It is a figure shown by.

  In FIG. 4, the horizontal axis represents the speed v (* 100 cm / s) at which the spin moves, and the vertical axis represents the signal intensity I. Here, in the preparation sequence PS shown in FIG. 3, the magnetization of the spin passing through the origin of the Gcrush axis moves at a constant linear motion on the Gcrush axis at the central time t1a at which the gradient pulse Gc1a is transmitted. When the magnetization of the spin is moving at a speed of 100 cm / s, it is assumed that the phase received by the gradient pulse Gc1b is π at the central time point t1b at which the gradient pulse Gc1b is transmitted. ing. Further, here, when the signal intensity is 1, it means that the magnetization has completely reached thermal equilibrium, and T2 attenuation is not considered.

  As shown in FIG. 4, in the present embodiment, the signal intensity obtained varies depending on the speed of the spin moving within the subject. Specifically, as shown in FIG. 4, for the first spin in a stationary state where the velocity is 0, the signal intensity is about 0.8, for example, for the second spin where the velocity is 100 cm / s. Gives a signal strength of about -0.2.

This phenomenon will be described. As described above, each of the spin echo signal SE2 and the stimulated echo signal STE generated at the central time tr4 (see FIG. 3) at the time t17 to t18 at which the fourth RF pulse RF4 is transmitted is the second state that is in the moving state. The phase of the spin is shifted according to the moving speed. Therefore, the phase theta _SE2 of the spin echo signal SE2, the phase theta _STE of stimulated red echo signal STE is when different in the moving speed, since that would cancel each other, the signal strength is affected. For this reason, as shown in FIG. 4, the signal intensity obtained differs according to the speed of the spin moving within the subject.

  Next, as shown in FIG. 2, an imaging sequence IS is performed (S21).

  Here, in the SSFP type imaging method, the scanning unit 2 executes the imaging sequence IS.

  FIG. 5 is a pulse sequence diagram showing an imaging sequence IS implemented in the first embodiment of the present invention.

  In FIG. 5, RF is a time axis for transmitting RF pulses, Gslice is a time axis for transmitting gradient pulses in the slice selection encoding direction, and Gread is a time axis for transmitting gradient pulses in the readout direction. Gwarp indicates a time axis for transmitting a gradient pulse in the phase encoding direction, and the horizontal axis indicates time t and the vertical axis indicates pulse intensity.

  As shown in FIG. 5, when performing the imaging sequence IS, the RF pulse RF is repeatedly transmitted to the subject SU. Here, the scan unit 2 transmits each RF pulse RF to the subject SU at a repetition time TR such that the longitudinal magnetization and transverse magnetization of the spin are in a steady state in the subject SU.

  Along with this, a slice selection gradient pulse Gs for selecting a slice of the subject SU excited by the RF pulse RF as an imaging region, and a phase for phase encoding the magnetic resonance signal generated in the slice excited by the RF pulse. The encode gradient pulse Gr and the frequency encode gradient pulse for frequency-encoding the magnetic resonance signal generated in the slice excited by the RF pulse are transmitted as gradient pulses to the subject SU within the repetition time TR. Here, the slice selection gradient pulse, the phase encode gradient pulse, and the frequency encode gradient pulse are transmitted to the subject SU so that the time integration value within the repetition time TR becomes zero. That is, as shown in FIG. 5, after collecting the magnetic resonance signal as imaging data, the transverse magnetization is rewound within the repetition time TR, and the phase encoded by the gradient magnetic field is reset.

  Next, as shown in FIG. 2, it is determined whether or not all the imaging data corresponding to the k space have been collected (S22).

  Here, the control unit 30 determines whether all the imaging data corresponding to the k space has been collected.

  If not all of the imaging data corresponding to the k space has been collected (No), as shown in FIG. 2, the preparation sequence PS (S11) and the imaging sequence IS (S21) are performed. Execute again sequentially. That is, by repeatedly performing the preparation sequence PS (S11) and the imaging sequence IS (S21), imaging data is collected until the entire k-space is filled.

  On the other hand, when all the imaging data has been collected so as to correspond to the k space (Yes), an image is generated as shown in FIG. 2 (S31).

  Here, imaging data obtained by the scanning unit 2 executing the imaging sequence IS is set as raw data, and the image generating unit 31 reconstructs an image of the subject SU.

  In the present embodiment, as described above, after the preparation sequence PS is performed, the signal intensity obtained according to the speed of the spin moving within the subject is different (see FIG. 4). The spin has a large longitudinal magnetization. For example, the longitudinal magnetization of the spin in a moving state moving at a speed of 100 cm / s becomes small, and there is a large difference. For this reason, in the image reconstructed based on the imaging data obtained by executing the imaging sequence IS after the execution of the preparation sequence PS, the image is high between the stationary state portion and the moving state portion. An image with contrast is generated. Specifically, an MRA image with high contrast is generated between an organ portion in which the spin is stationary and a blood portion in which the spin is moving.

  Next, as shown in FIG. 2, an image is displayed (S41).

  Here, the display unit 33 receives data about the image of the subject SU from the image generation unit 31 and displays the image on the display screen.

  As described above, in the present embodiment, the preparation sequence PS that transmits the preparation pulse to the subject so that the signal intensity of the magnetic resonance signal obtained in accordance with the speed of the spin moving in the subject is different from the imaging sequence IS. To be implemented before Here, the first RF pulse RF1, the second RF pulse RF2, the third RF pulse RF3, and the fourth RF pulse RF4 are sequentially transmitted to the subject as preparation pulses. Along with this, the crusher gradient pulses Gc1, Gc2 are transmitted to the subject so that the time points tr2, tr3 at which the second RF pulse RF2 and the third RF pulse RF3 are transmitted are sandwiched on the time axis t. Then, after transmitting the fourth RF pulse RF4 and after transmitting the crusher gradient pulses Gc1 and Gc2, the killer gradient pulse Gk is transmitted to the subject. For this reason, as described above, after the preparation sequence PS is performed, the signal intensity obtained according to the speed of the spin moving within the subject differs, so the imaging sequence IS is executed after the preparation sequence PS is performed. In the image reconstructed based on the imaging data obtained by doing so, an image with different luminance is generated according to the speed at which the spin moves.

  For this reason, as described above, the present embodiment can obtain an image in which a portion that moves at a predetermined moving speed in the subject SU is emphasized. For example, an MRA image having a high contrast can be generated between an organ portion in which the spin is stationary and a blood portion in which the spin is moving. This is because the crusher gradient pulses Gc1 and Gc2 change the amount of dephasing between the stimulated echo signal and the spin echo signal due to the magnetization of the spin moving in the Gcrush direction, and the signal intensity decreases. This is because flow voids are generated.

  Furthermore, since the application time of the preparation pulse is short, it can be used for various applications.

  In the present embodiment, the first RF pulse RF1 and the fourth RF pulse RF4 are transmitted as 90 ° x pulses and −90 ° x pulses. For this reason, the magnetization due to the spin in the stationary state can be maintained, and the magnetization of the spin in the moving state can be distributed to an intensity between 0 or less and 1 so that a high-contrast image can be obtained according to the moving speed of the spin. Can be generated.

  Therefore, this embodiment can improve versatility without using a contrast agent, and can improve image quality.

<Embodiment 2>
Hereinafter, Embodiment 2 according to the present invention will be described.

  FIG. 6 is a pulse sequence diagram showing the preparation sequence PS in the second embodiment according to the present invention.

  In FIG. 6, (a) is a time axis for transmitting the RF pulse RF, (b) is a time axis for transmitting the crusher gradient pulse Gcrush as a gradient pulse, and (c) is a gradient pulse. The time axis which transmits the killer gradient pulse Gkill is shown, and the horizontal axis indicates time t and the vertical axis indicates the pulse intensity. Here, each of Gcrush and Gkill is at least one axial direction of the slice selection direction, the phase encoding direction, and the frequency encoding direction.

  As shown in FIG. 6, the present embodiment is different from the first embodiment in the preparation sequence PS that is performed when the subject SU is imaged. Except for this point, the second embodiment is the same as the first embodiment. For this reason, description is abbreviate | omitted about the overlapping location.

  When the preparation sequence PS is executed, as shown in FIGS. 6A, 6B, and 6C, the first RF pulse RF1 and the first pulse are prepared as the preparation pulses, as in the first embodiment. The scanning unit 2 transmits the 2RF pulse RF2, the third RF pulse RF3, the fourth RF pulse RF4, the first crusher gradient pulse Gc1, the second crusher gradient pulse Gc2, and the killer pulse Gk to the subject SU. To do.

  However, as shown in FIG. 6A, in the present embodiment, unlike the first embodiment, a plurality of RF pulses RF21 and RF22 including a 180 ° pulse are transmitted as the second RF pulse RF2, and the 180 ° pulse is transmitted. A plurality of RF pulses RF31 and RF32 including are transmitted as a third RF pulse RF3.

  Here, the plurality of RF pulses RF21, RF22, RF31, and RF32 transmitted as the second RF pulse RF2 and the third RF pulse RF3 have the same phase and the same absolute value of the flip angle. Yes, so that the sign is reversed.

  In the present embodiment, as the plurality of RF pulses RF21, RF22, RF31, and RF32 transmitted in each of the second RF pulse RF2 and the third RF pulse RF3, α ° pulses RF21, RF31 other than 180 ° pulses, and 180 ° pulses are used. RF22 and RF32 are sequentially transmitted.

  Specifically, as shown in FIG. 6A, as the plurality of RF pulses RF21 and RF22 transmitted as the second RF pulse RF2, the absolute value of the flip angle is 90 °, the sign is positive, and the phase is positive. Is transmitted as a first α ° pulse RF21, the absolute value of the flip angle is 180 °, the sign is positive, and the 180 ° y pulse whose phase is in the y direction is transmitted. The first 180 ° pulse RF22 is transmitted. That is, as the plurality of RF pulses RF21 and RF22 transmitted as the second RF pulse RF2, the first α ° pulse RF21 other than the 180 ° pulse and the first 180 ° pulse RF22 are spun along the xz plane. Send to flip.

  Further, as shown in FIG. 6A, as the plurality of RF pulses RF31 and RF32 transmitted as the third RF pulse RF3, the absolute value of the flip angle is 90 °, the sign is negative, and the phase is in the y direction. A -90 ° y pulse is transmitted as the second α ° pulse RF31, and the absolute value of the flip angle is 180 °, the sign is negative, and the phase is in the y direction. Transmit as a second 180 ° pulse RF22. That is, as the plurality of RF pulses RF31 and RF32 transmitted as the third RF pulse RF3, the second α ° pulse RF31 having the same flip angle as that of the first α ° pulse RF21, other than the 180 ° pulse, and the second The 180 ° pulse RF32 is transmitted so that the spin is flipped along the xz plane in the direction opposite to the direction flipped by the transmission of the second RF pulse RF2.

  Here, as shown in FIG. 6 (a), between the central time point tr1 of the time t11 to t12 for transmitting the first RF pulse RF1 and the central time point tr21 of the time t13 to t131 for transmitting the first α ° pulse RF21. For the fourth time interval τ4, the central time point tr21 of the time t13 to t131 at which the first α ° pulse RF21 is transmitted and the central time point tr22 of the time t140 to t14 at which the first 180 ° pulse RF22 is transmitted. The first RF pulse RF1 and the first α ° pulse RF21 and the first 180 ° pulse RF22 as the second RF pulse RF2 are sequentially changed so that the fifth time interval τ5 between them is doubled. Send to the subject. Then, with respect to the fourth time interval τ4, the central time point tr22 of the time t140 to t14 for transmitting the first 180 ° pulse RF22 and the central time point tr31 of the time t15 to t151 for transmitting the second α ° pulse RF31. And the sixth time interval τ6 between the second α ° pulse RF31 and the center time tr31 of the time t15 to t151 for transmitting the second α ° pulse RF31 and the time t160 to t16 for transmitting the second 180 ° pulse RF32 The seventh time interval τ7 between the central time point tr32 is double, and the central time point tr32 and the fourth RF pulse RF4 are transmitted at times t17 to t18 at the time t160 to t16 when the second 180 ° pulse RF32 is transmitted. And the second α ° pulse RF31 as the third RF pulse RF3 and the second time interval τ8 so that the eighth time interval τ8 from the central time tr4 of And 180 ° pulses Rf32, the each of the first 4RF pulse RF4, sequentially transmits to the subject.

  As shown in FIG. 6B, in the present embodiment, in the preparation pulse in the preparation sequence PS, the first crusher gradient pulse Gc1 and the second crusher gradient pulse Gc2 are the same as in the first embodiment. , A pair of gradient pulses Gc11a, Gc11b, Gc12a, Gc12b, Gc21a, Gc21b, Gc22a, Gc11a, Gc11b, Gc12a, Gc12b, Gc22a, Gc11a, Gc11b, Gc12b, Gc12b, It is transmitted to the subject as Gc22b.

  Specifically, the time integration value of the gradient pulse Gc11a is D11a, the time integration value of the gradient pulse Gc11b is D11b, the time integration value of the gradient pulse Gc12a is D12a, the time integration value of the gradient pulse Gc12b is D12b, and the time of the gradient pulse Gc21a is When the integrated value is D21a, the time integrated value of the gradient pulse Gc21b is D21b, the time integrated value of the gradient pulse Gc22a is D22a, and the time integrated value of the gradient pulse Gc22b is D22b, the following formula (2) is satisfied. The gradient pulses Gc11a, Gc11b, Gc12a, Gc12b, Gc21a, Gc21b, Gc22a, and Gc22b are transmitted as the first crusher gradient pulse Gc1 and the second crusher gradient pulse Gc2.

  2 * D11a = D11b + D12a = D12b + D21a = D21b + D22a = 2 * D22b (2)

  In the present embodiment, as shown in FIG. 6B, each of a pair of gradient pulses Gc11a, Gc11b, Gc12a, Gc12b constituting the first crusher gradient pulse Gc1 and a second crusher gradient pulse Gc2 are configured. The pair of gradient pulses Gc21a, Gc21b, Gc22a, and Gc22b are transmitted so that the time integration values are the same and have the same polarity. That is, D11a, D11b, D12a, D12b, D21a, D21b, D22a, D22b are all made the same.

  Here, as shown in FIG. 6B, each of the pair of gradient pulses Gc11a, Gc11b, Gc12a, Gc12b constituting the first crusher gradient pulse Gc1 transmits the second RF pulse RF2 at times t13 to t14. Each of the pair of gradient pulses Gc11a, Gc11b, Gc12a, and Gc12b is transmitted so as to be symmetrically arranged on the time axis t with the central time point tr2 as the central axis. That is, the pair of gradient pulses Gc11a and Gc11b are sequentially transmitted so that the central time points tr21 of the time t13 to t131 for transmitting the first α ° pulse RF21 in the second RF pulse RF2 are arranged symmetrically with respect to the time axis. Then, the pair of gradient pulses Gc12a and Gc12b are sequentially transmitted so that the central time points tr22 of the times t140 to t14 for transmitting the first 180 ° pulse RF22 are arranged symmetrically with respect to the time axis.

  Further, as shown in FIG. 6 (b), each of a pair of gradient pulses Gc21a, Gc21b, Gc22a, Gc22b constituting the second crusher gradient pulse Gc2 is the center of time t15 to t16 at which the third RF pulse RF3 is transmitted. Each of the pair of gradient pulses Gc21a, Gc21b, Gc22a, Gc22b is transmitted so as to be arranged symmetrically with respect to the time axis t with the time point tr3 as the central axis. That is, the pair of gradient pulses Gc21a and Gc21b are sequentially transmitted so that the central time points tr31 of the times t15 to t151 for transmitting the second α ° pulse RF31 in the third RF pulse RF3 are arranged symmetrically with respect to the time axis. Then, the pair of gradient pulses Gc22a and Gc22b are sequentially transmitted so that the central time points tr32 of the times t160 to t16 for transmitting the second 180 ° pulse RF32 are arranged symmetrically with respect to the time axis.

  FIG. 7 is a graph showing the result of simulating the relationship between the signal intensity obtained at time t19 after execution of the preparation sequence PS and the speed of the spin moving within the subject in the second embodiment according to the present invention. It is a figure shown by.

  In FIG. 7, the horizontal axis represents the speed v (* 100 cm / s) at which the spin moves, and the vertical axis represents the signal intensity I. The simulation was performed in the same manner as in the first embodiment.

  As shown in FIG. 7, like the first embodiment, the present embodiment differs in the signal intensity obtained according to the speed of the spin moving within the subject. Specifically, as shown in FIG. 7, the stationary first spin whose velocity is 0 has a signal intensity of about 1.0, for example, the second spin whose velocity is 85 cm / s. Gives a signal strength of about -0.1.

  As described above, in the present embodiment, the plurality of RF pulses RF21 and RF22 including the 180 ° pulse are transmitted as the second RF pulse RF2, and the plurality of RF pulses RF31 and RF32 including the 180 ° pulse are transmitted to the third RF pulse. Transmit as pulse RF3. For this reason, this embodiment can obtain an image in which a portion moving at a predetermined moving speed in the subject SU is emphasized, as in the first embodiment. For example, an MRA image having a high contrast can be generated between an organ portion in which the spin is stationary and a blood portion in which the spin is moving.

  In particular, in the present embodiment, with respect to the magnetization of a stationary spin with a velocity of 0, the spin echo signal and the stimulated echo signal are completely refocused by the 180 ° y pulse. Since the intensity is obtained as about 1.0, it is easy to generate an image with higher luminance than in the first embodiment.

  Therefore, as in the first embodiment, this embodiment can improve versatility without using a contrast agent, and can improve image quality.

<Embodiment 3>
Hereinafter, Embodiment 3 according to the present invention will be described.

  FIG. 8 is a pulse sequence diagram showing the preparation sequence PS in the third embodiment of the present invention.

  In FIG. 8, (a) is a time axis for transmitting the RF pulse RF, (b) is a time axis for transmitting the crusher gradient pulse Gcrush as a gradient pulse, and (c) is as a gradient pulse. The time axis which transmits the killer gradient pulse Gkill is shown, and the horizontal axis indicates time t and the vertical axis indicates the pulse intensity. Here, each of Gcrush and Gkill is at least one axial direction of the slice selection direction, the phase encoding direction, and the frequency encoding direction.

  As shown in FIG. 8, in the present embodiment, the absolute value of the flip angle between the first α ° pulse RF21 and the second α ° pulse RF31 in the preparation sequence PS performed when imaging the subject SU. Is different from the second embodiment. Except for this point, the second embodiment is the same as the second embodiment. For this reason, description is abbreviate | omitted about the overlapping location.

  In the present embodiment, as shown in FIG. 8A, unlike the second embodiment, the absolute value of the flip angle between the first α ° pulse RF21 and the second α ° pulse RF31 is 120 °. That is, the first α ° pulse RF21 is transmitted as a 120 ° y pulse, and the second α ° pulse RF31 is transmitted as a −120 ° y pulse.

  FIG. 9 is a graph showing a simulation result of the relationship between the signal intensity obtained at time t19 after execution of the preparation sequence PS and the speed of the spin moving within the subject in the second embodiment according to the present invention. It is a figure shown by.

  In FIG. 9, the horizontal axis represents the speed v (* 100 cm / s) at which the spin moves, and the vertical axis represents the signal intensity I. The simulation was performed in the same manner as in the first embodiment.

  As shown in FIG. 9, as in the second embodiment, the present embodiment differs in the signal intensity obtained according to the speed of the spin moving within the subject. Specifically, as shown in FIG. 9, the stationary first spin with a velocity of 0 has a signal intensity of about 1.0, for example, the second spin with a velocity of 75 cm / s. Gives a signal strength of about 0.3.

  As described above, in the present embodiment, as in the second embodiment, the plurality of RF pulses RF21 and RF22 including the 180 ° pulse are transmitted as the second RF pulse RF2, and the plurality of RF pulses including the 180 ° pulse are included. RF31 and RF32 are transmitted as the third RF pulse RF3. In particular, since the absolute value of the flip angle between the first α ° pulse RF21 and the second α ° pulse RF31 is 120 °, the generation amount of the stimulated echo signal can be increased. The effect of the pulses Gc1 and Gc2 can be enhanced.

  Therefore, as in the second embodiment, the present embodiment can improve versatility without using a contrast agent, and can improve image quality.

<Embodiment 4>
Hereinafter, Embodiment 4 according to the present invention will be described.

  FIG. 10 is a pulse sequence diagram showing the preparation sequence PS in the fourth embodiment according to the present invention.

  10A is a time axis for transmitting the RF pulse RF, FIG. 10B is a time axis for transmitting the crusher gradient pulse Gcrush as a gradient pulse, and FIG. 10C is a time axis for transmitting the gradient pulse. The time axis for transmitting the killer gradient pulse Gkill is shown, (d) shows the time axis for transmitting the velocity encode gradient pulse Gvenc as the gradient pulse, and the horizontal axis is time t, The vertical axis represents the pulse intensity. Here, each of Gcrush, Gkill, and Gvenc is at least one axial direction of the slice selection direction, the phase encoding direction, and the frequency encoding direction.

  As shown in FIG. 10, unlike the third embodiment, the present embodiment transmits a velocity encoding gradient pulse Gvenc in a preparation sequence PS that is performed when imaging the subject SU. Except for this point, the second embodiment is the same as the third embodiment. For this reason, description is abbreviate | omitted about the overlapping location.

  As shown in FIG. 10A, the scan unit 2 transmits a velocity encode gradient pulse Gvenc as a preparation pulse so that the phase of the spin varies according to the speed of the spin moving in the spin of the subject. Shift. That is, in the spin of the subject, the phase of the spin in a stationary state at a first velocity of 0 and the phase of a spin in a moving state moving at a second velocity different from the first velocity The velocity encode gradient pulse is transmitted as a preparation pulse so as to be shifted from each other.

  Here, the velocity encode gradient pulse Gvenc is transmitted so as to be a pair of gradient pulses having opposite polarities on the time axis t with the central time point tv at which the velocity encode gradient pulse Gvenc is transmitted as an axis.

  As described above, in this embodiment, the velocity encode gradient pulse Gvenc is transmitted. For this reason, it is possible to shift the phase of the spin to be different depending on the speed of the spin moving in the spin of the subject. For this reason, the present embodiment can more effectively obtain an image in which a portion that moves at a predetermined moving speed in the subject SU is emphasized. That is, it is possible to generate flow voids in multi-axis directions and perform flow spoiling with quantitativeness.

  Therefore, as in the third embodiment, this embodiment can improve versatility without using a contrast agent, and can improve image quality.

<Embodiment 5>
The fifth embodiment according to the present invention will be described below.

  In the present embodiment, after performing the first preparation pulse sequence PS1 as the preparation sequence PS, the scanning unit 2 acquires the magnetic resonance signal generated by executing the imaging sequence IS as the first imaging data. At the same time, the first preparation except that the crusher gradient pulses Gc1 and Gc2 and the velocity encode gradient pulse Gvenc are not transmitted and the flip angles of the second RF pulse RF2 and the third RF pulse RF3 are different. After performing the second preparation pulse sequence PS2 that transmits the same preparation pulse as the sequence PS, the scanning unit 2 acquires a magnetic resonance signal generated by performing the imaging sequence IS as second imaging data.

  Then, the image generation unit 31 generates a first image based on the first imaging data, and the image generation unit 31 generates a second image based on the second imaging data. Thereafter, the difference image generated by performing the difference process between the generated first image and the second image is set as an image of the subject.

  The present embodiment is the same as the fourth embodiment except for the above points. For this reason, description is abbreviate | omitted about the overlapping part.

  FIG. 11 is a flowchart showing an operation when imaging the subject SU in the fifth embodiment of the present invention.

  First, as shown in FIG. 11, a first image is generated for a subject (S111).

  FIG. 12 is a flowchart showing an operation of generating a first image for a subject in the fifth embodiment of the present invention.

  As shown in FIG. 12, first, the first preparation pulse sequence PS1 is performed (S11a).

  Here, the scanning unit 2 performs the first preparation pulse sequence PS1.

  FIG. 13 is a pulse sequence diagram showing a first preparation pulse sequence PS1 in Embodiment 5 according to the present invention.

  In FIG. 13, (a) is a time axis RF for transmitting an RF pulse, and (b), (c) and (d) are respectively a plurality of axial directions G1, G2, G3 for transmitting gradient pulses. The horizontal axis indicates time t, and the vertical axis indicates pulse intensity. Here, G1, G2, and G3 are axial directions in which gradient pulses are transmitted, and indicate axial directions corresponding to any of the slice selection direction, the phase encoding direction, and the frequency encoding direction.

  As shown in FIG. 13A, FIG. 13B, FIG. 13C, and FIG. 13D, in the present embodiment, unlike the preparation sequence PS implemented in the fourth embodiment, the first A crusher gradient pulse Gc1 and a second crusher gradient pulse Gc2 are transmitted in a plurality of axial directions G2 and G3. Further, the velocity encode gradient pulse Gvenc is transmitted in a plurality of axial directions G1, G2, and G3. Except for this point, it is the same as the preparation sequence PS implemented in the fourth embodiment.

  In the present embodiment, as shown in FIGS. 13B, 13C, and 13D, as the velocity encode gradient pulse Gvenc, the first velocity encode gradient pulse Gvenc1 and the second velocity encode gradient pulse. Each of Gvenc2 and the third velocity encode gradient pulse Gvenc3 is transmitted to the three axial directions G1, G2, and G3 as in the fourth embodiment. Here, the first velocity encode gradient pulse Gvenc1 is transmitted at the sixth time interval τ6 in the first axial direction G1. Then, the second velocity encode gradient pulse Gvenc2 is transmitted at the seventh time interval τ7 in the second axial direction G2. The third velocity encode gradient pulse Gvenc3 is transmitted at the seventh time interval τ7 in the third axial direction G3.

  And as shown in Drawing 13 (c) and Drawing 13 (d), about 1st crusher gradient pulse Gc1 and 2nd crusher gradient pulse Gc2, among three axial directions G1, G2, G3, Similarly to the fourth embodiment, the transmission is performed in two axial directions, ie, the second axial direction G2 and the third axial direction G3.

  Here, as shown in FIG. 13C and FIG. 13D, the seventh time interval τ7 for transmitting the second α ° pulse RF31 and the second 180 ° pulse RF32 as the third RF pulse RF3. In order to transmit the second velocity encode gradient pulse Gvenc2 and the third velocity encode gradient pulse Gvenc3, gradient pulses Gc21b, Gc22a transmitted as the second crusher gradient pulse Gc2 in the seventh time interval τ7, Transmission with the 2 speed encoding gradient pulse Gvenc2 and the 3rd speed encoding gradient pulse Gvenc3 overlaps. For this reason, as shown in FIGS. 13C and 13D, the gradient pulses Gc21b and Gc22a transmitted as the second crusher gradient pulse Gc2 in the seventh time interval τ7 are indicated by dotted lines. The pulse shape obtained by adding both is indicated by a solid line.

  Then, after the execution of the first preparation pulse sequence PS1, the signal intensity due to the spin moves in the plurality of axial directions G2 and G3 in accordance with the speed of the spin moving within the subject as in the fourth embodiment. Obtained differently.

  Next, as shown in FIG. 12, the imaging sequence IS is performed (S21a).

  Here, as in the fourth embodiment, the scan unit 2 executes the imaging sequence IS in the SSFP type imaging method.

  Next, as shown in FIG. 12, it is determined whether or not all the imaging data corresponding to the k space have been collected (S22a).

  Here, as in the fourth embodiment, the control unit 30 determines whether all the imaging data corresponding to the k space has been collected. In the present embodiment, imaging data is collected as first imaging data. If not all the imaging data corresponding to the k space has been collected (No), as shown in FIG. 12, the execution of the preparation sequence PS (S11a) and the execution of the imaging sequence IS (S21a) are performed. Execute again sequentially.

  On the other hand, when all the imaging data are collected so as to correspond to the k space (Yes), as shown in FIG. 12, the first image I1 is generated (S31a).

  Here, as in the fourth embodiment, the first imaging data obtained as imaging data by the scan unit 2 executing the imaging sequence IS is set as raw data, and the image generation unit 31 displays an image of the subject SU. Reconstructed as the first image I1.

  Next, as shown in FIG. 11, a second image is generated for the subject (S121).

  FIG. 14 is a flowchart showing an operation of generating a second image for a subject in the fifth embodiment according to the present invention.

  As shown in FIG. 14, first, the second preparation pulse sequence PS2 is performed (S11b).

  Here, the scanning unit 2 performs the second preparation pulse sequence PS2.

  FIG. 15 is a pulse sequence diagram showing the second preparation pulse sequence PS2 in the fifth embodiment according to the invention.

  In FIG. 15, (a) is a time axis RF for transmitting an RF pulse, and (b), (c) and (d) are respectively a plurality of axial directions G1, G2, G3 for transmitting gradient pulses. The horizontal axis indicates time t, and the vertical axis indicates pulse intensity. Here, G1, G2, and G3 are axial directions in which gradient pulses are transmitted, and indicate axial directions corresponding to any of the slice selection direction, the phase encoding direction, and the frequency encoding direction.

  As shown in FIGS. 15 (a), 15 (b), 15 (c), and 15 (d), the second preparation pulse sequence PS2 is different from the first preparation pulse sequence PS1 described above, and the crusher. The gradient pulses Gc1 and Gc2 and the velocity encode gradient pulse Gvenc are not transmitted. Further, the flip angles of the second RF pulse RF2 and the third RF pulse RF3 are different. Except for this point, it is the same as the first preparation pulse sequence PS1.

  In the present embodiment, as shown in FIG. 15A, unlike the first preparation pulse sequence PS1, the absolute value of the flip angle between the first α ° pulse RF21 and the second α ° pulse RF31 is 180. °. That is, the first α ° pulse RF21 is transmitted as a 180 ° y pulse, and the second α ° pulse RF31 is transmitted as a −180 ° y pulse.

  Further, as shown in FIGS. 15B, 15C, and 15D, unlike the first preparation pulse sequence PS1, the first velocity encode gradient pulse Gvenc1, the second velocity encode gradient pulse Gvenc2, and so on. The third velocity encode gradient pulse Gvenc3 is not transmitted. Further, as shown in FIGS. 15C and 15D, the first crusher gradient pulse Gc1 and the second crusher gradient pulse Gc2 are not transmitted.

  Then, after the execution of the second preparation pulse sequence PS2, unlike the case of the first preparation pulse sequence PS1, the signal intensity due to the spin does not change depending on the speed of the spin moving within the subject. Is obtained as follows.

  Next, as in the case where the first image I1 is generated, the imaging sequence IS is performed as shown in FIG. 14 (S21b). Then, in the same manner as when the first image I1 is generated, it is determined whether or not all the imaging data corresponding to the k space has been collected (S22b), and all the imaging data is collected so as to correspond to the k space. If it is (Yes), the second image I2 is generated (S31b).

  Next, as shown in FIG. 11, a difference image SI is generated by performing a difference process between the first image I1 and the second image I2 (S131).

  Here, the image generation unit 31 performs a difference process on the first image I1 and the second image I2 generated for the same slice plane in the subject as described above, and generates a difference image based on the difference value. To do. For example, a process of calculating a difference value by performing a difference between pixel values of pixels at positions corresponding to each other in the first image I1 and the second image I2 is performed for each pixel. And the difference image SI is produced | generated by arrange | positioning the difference value obtained for every pixel in a corresponding pixel position. Here, the difference image SI may be generated by performing the difference processing with the complex data as it is.

  Next, as shown in FIG. 11, the difference image SI is displayed (S141).

  Here, the display unit 33 receives the data of the difference image SI generated as described above from the image generation unit 31, and displays the difference image on the display screen.

  As described above, in the present embodiment, the magnetic resonance signal generated by performing the imaging sequence after the first preparation pulse sequence PS1 corresponding to the preparation pulse sequence PS of the fourth embodiment is used as the first imaging. Get as data. Then, the first preparation pulse sequence PS1 except that the crusher gradient pulses Gc1 and Gc2 and the velocity encode gradient pulse Gvenc are not transmitted and the flip angles of the second RF pulse RF2 and the third RF pulse RF3 are different. After executing the second preparation pulse sequence PS2 for transmitting the same preparation pulse as described above, a magnetic resonance signal generated by executing the imaging sequence is acquired as second imaging data. Then, a first image is generated based on the first imaging data, and a second image is generated based on the second imaging data. Thereafter, a difference image is generated by performing difference processing between the first image and the second image.

  In the present embodiment, similarly to the fourth embodiment, the first image I1 can be generated as an image in which the signal intensity from the spin in the moving state is suppressed with respect to the spin in the stationary state. That is, an image in which the flow of blood or the like flowing in the subject is suppressed. On the other hand, as in the fourth embodiment, the second image I2 is generated as an image that does not suppress the signal intensity from the spinning spin. That is, the image is not suppressed in flow. For this reason, the difference image SI generated by performing the difference process between the first image I1 and the second image I2 corresponds to the MRA image in which the flow is emphasized because the signal intensity from the spin in the moving state corresponds to the difference value. It becomes. In particular, in the present embodiment, since the second preparation pulse sequence PS2 is executed as the preparation sequence even when the second image I2 is generated, it is possible to prevent the contrast from changing. . Furthermore, since the signal from the flow such as the artery may be rotated 180 ° by the velocity encode gradient pulse Gvenc and have a negative value, the absolute value of the signal corresponding to the flow in the difference image SI is the first image I1. And the S / N ratio can be improved. For this reason, in the difference image SI, the enhancement of the flow is displayed with high accuracy.

  Further, the amount of signal attenuation by performing the first preparation pulse sequence PS1 as described above can be easily calculated from the area (time integration value) of the gradient pulses of the crusher gradient pulses Gc1, Gc2 and the velocity encode gradient pulse Gvenc. . For this reason, for example, by measuring the moving speed of the flow by the phase contrast method or the like, it is possible to easily generate an image that emphasizes the necessary flow as appropriate.

  Further, in the second preparation pulse sequence PS2, since the gradient pulse is not transmitted, the flow flowing in the slice selection direction can be easily depicted. In the first preparation pulse sequence PS1, since the gradient pulses of the crusher gradient pulses Gc1 and Gc2 and the velocity encode gradient pulse Gvenc can be transmitted in a plurality of axial directions, all flows flowing in the respective axial directions can be drawn. it can.

  Therefore, this embodiment can improve versatility without using a contrast agent, and can improve image quality.

<Embodiment 6>
The sixth embodiment according to the present invention will be described below.

  FIG. 16 is a diagram illustrating a state in which the preparation sequence PS and the imaging sequence IS are performed in the sixth embodiment according to the present invention. In FIG. 16, the horizontal axis is the time axis t, (a) shows the transition of the heartbeat signal ECG of the subject, and (b) shows the pulse to be transmitted in the execution of the preparation sequence PS and the imaging sequence IS. The timing is shown corresponding to the heartbeat signal ECG of the subject.

  In the present embodiment, as shown in FIG. 16, the timing for executing the preparation sequence PS and the imaging sequence IS is specified. In addition, before transmitting the first RF pulse RF1 as the preparation pulse in the preparation sequence PS, the killer gradient pulse Gk0 is transmitted so as to generate a gradient magnetic field that causes the transverse magnetization of the spin to disappear in the subject. Except for this point, the second embodiment is the same as the fourth embodiment. For this reason, description is abbreviate | omitted about the overlapping location.

  In the present embodiment, as shown in FIG. 16, the scan unit 2 performs the preparation sequence PS so as to correspond to the cardiac systole SY in the heartbeat exercise of the subject, and then enters the diastole SK in the heartbeat exercise. The imaging sequence IS is performed in a corresponding manner.

  Specifically, first, the flow rate of fluid such as blood flowing in the subject is measured using a phase contrast method synchronized with the heart rate, and the systolic SY and diastole SK in the heartbeat movement of the subject are measured. Identify timing. Thereafter, as shown in FIG. 16, the preparation sequence PS and the imaging sequence IS are performed so as to correspond to the specified timing.

  As described above, the present embodiment easily distinguishes blood from other stationary portions in order to perform the preparation sequence PS during the systole, which is a state in which the blood movement speed is high in the heartbeat movement of the subject. be able to. In addition, since the imaging sequence IS is performed during the diastole in which the blood moving speed is low, it is possible to suppress the occurrence of body movement artifacts in the imaged image. Furthermore, in the diastole period, since the slow flow time is a long time of several hundreds msec, it is possible to sufficiently acquire imaging data. Further, in this embodiment, since the transverse magnetization of the spin is lost by the killer gradient pulse Gk0 before transmitting the first RF pulse RF1, the image quality can be further improved.

  The magnetic resonance imaging apparatus 1 of the above embodiment corresponds to the magnetic resonance imaging apparatus of the present invention. The scanning unit 2 in the above embodiment corresponds to the scanning unit of the present invention. The image generation unit 31 in the above embodiment corresponds to the image generation unit of the present invention. Moreover, the display part 33 of said embodiment is corresponded to the display part of this invention.

  In implementing the present invention, the present invention is not limited to the above-described embodiment, and various modifications can be employed.

  For example, when an RF pulse is transmitted as a preparation pulse, the value is not limited to the above-described flip angle value. In this case, slice selection may be performed. Further, a fat suppression method such as CHESS (Chemical Shift Selective) method or Spectral IR method may be used in combination. Further, the T2 contrast may be adjusted by adjusting the time between the first RF pulse RF1 and the fourth RF pulse RF4.

  In the above embodiment, a case has been described in which a rectangular pulse having a wide frequency band and effective against static magnetic field inhomogeneity is transmitted as an RF pulse. However, the present invention is not limited to this.

  Further, for example, when transmitting a velocity encode gradient pulse as a preparation pulse, it may be transmitted to an arbitrary plurality of axes. Moreover, you may transmit in arbitrary areas, and you may transmit in arbitrary frequency in addition.

  In addition, for example, the imaging sequence may be implemented by various methods such as FSE (Fast Spin Echo), SE (Spin Echo), GRE (Gradient Recalculated Echo), and SPGR (Spoiled GRASS) in addition to the SSFP method. Good. In particular, it is preferable to apply to three-dimensional imaging.

  Further, for example, the flip angle, phase, and transmission timing of the first RF pulse RF1, the second RF pulse RF2, the third RF pulse RF3, and the fourth RF pulse RF4 can be arbitrarily set.

  Further, the present invention may be applied when the above scan is performed in synchronization with the respiratory motion of the subject. Here, for example, it is preferable to perform the scan so as to be synchronized with the state of expiration or inspiration.

  In the above preparation sequence PS, the signal intensity due to the magnetization of the spin moving at the specific flow rate is attenuated to maintain the signal intensity due to the magnetization of the spin in the stationary state, and the signal intensity of the magnetization at the specific flow rate is attenuated. The present invention may also be applied to cases where the signal strength of other magnetizations is maintained.

FIG. 1 is a configuration diagram illustrating a configuration of a magnetic resonance imaging apparatus 1 according to the first embodiment of the present invention. FIG. 2 is a flowchart showing an operation when imaging the subject SU in the first embodiment according to the present invention. FIG. 3 is a pulse sequence diagram showing the preparation sequence PS in the first embodiment according to the present invention. FIG. 4 is a graph showing a simulation result of the relationship between the signal intensity obtained at time t19 after execution of the preparation sequence PS and the speed of the spin moving within the subject in the first embodiment according to the present invention. It is a figure shown by. FIG. 5 is a pulse sequence diagram showing an imaging sequence IS implemented in the first embodiment of the present invention. FIG. 6 is a pulse sequence diagram showing the preparation sequence PS in the second embodiment according to the present invention. FIG. 7 is a graph showing the result of simulating the relationship between the signal intensity obtained at time t19 after execution of the preparation sequence PS and the speed of the spin moving within the subject in the second embodiment according to the present invention. It is a figure shown by. FIG. 8 is a pulse sequence diagram showing the preparation sequence PS in the third embodiment of the present invention. FIG. 9 is a graph showing a simulation result of the relationship between the signal intensity obtained at time t19 after execution of the preparation sequence PS and the speed of the spin moving within the subject in the second embodiment according to the present invention. It is a figure shown by. FIG. 10 is a pulse sequence diagram showing the preparation sequence PS in the fourth embodiment according to the present invention. FIG. 11 is a flowchart showing an operation when imaging the subject SU in the fifth embodiment of the present invention. FIG. 12 is a flowchart showing an operation of generating a first image for a subject in the fifth embodiment of the present invention. FIG. 13 is a pulse sequence diagram showing a first preparation pulse sequence PS1 in Embodiment 5 according to the present invention. FIG. 14 is a flowchart showing an operation of generating a second image for a subject in the fifth embodiment according to the present invention. FIG. 15 is a pulse sequence diagram showing the second preparation pulse sequence PS2 in the fifth embodiment according to the invention. FIG. 16 is a diagram illustrating a state in which the preparation sequence PS and the imaging sequence IS are performed in the sixth embodiment according to the present invention.

Explanation of symbols

1: Magnetic resonance imaging apparatus (magnetic resonance imaging apparatus),
2: Scan part (scan part),
3: Operation console part,
12: Static magnetic field magnet section,
13: Gradient coil part,
14: RF coil section,
15: Cradle,
22: RF drive unit,
23: Gradient drive unit,
24: Data collection unit,
30: control unit,
31: Image generation unit (image generation unit),
32: Operation unit,
33: Display unit (display unit),
34: Storage unit
B: Imaging space

Claims (15)

An imaging sequence for obtaining, as imaging data, a magnetic resonance signal generated from a spin excited by the subject in a static magnetic field space, and an image of the subject based on the imaging data obtained by performing the imaging sequence A magnetic resonance imaging apparatus for generating
A preparation sequence for performing the imaging sequence and transmitting a preparation pulse to the subject so that the signal intensity of the magnetic resonance signal differs according to the speed of the spin moving in the subject is measured before the imaging sequence is performed. Including a scanning unit
The scanning unit, as the preparation pulse,
Each of the first RF pulse, the second RF pulse, the third RF pulse, and the fourth RF pulse is sequentially transmitted to the subject,
Transmitting a first crusher gradient pulse consisting of a pair of gradient pulses to the subject so as to sandwich the time point at which the RF pulse is transmitted as the second RF pulse in the time axis;
Transmitting a second crusher gradient pulse consisting of a pair of gradient pulses to the subject so as to sandwich the time point at which the RF pulse is transmitted as the third RF pulse in the time axis;
After transmitting the fourth RF pulse, transmitting a killer gradient pulse to the subject;
A first time interval between a central time point of transmitting the first RF pulse and a central time point of transmitting the second RF pulse; and a central time point of transmitting the second RF pulse and the first time point. The second time interval between the central time point for transmitting the 3RF pulse is doubled, and the central time point for transmitting the third RF pulse and the central time point for transmitting the fourth RF pulse. The third time interval between is the same,
Magnetic resonance imaging device. The scan unit transmits the first RF pulse and the fourth RF pulse so that their phases are the same, the absolute values of the flip angles are the same, and the signs are reversed.
The magnetic resonance imaging apparatus according to claim 1. The scanning unit transmits the first RF pulse and the fourth RF pulse so that the absolute value of the flip angle is 90 °.
The magnetic resonance imaging apparatus according to claim 1 or 2. The scanning unit transmits each of the second RF pulse and the third RF pulse so that the phases thereof are orthogonal to the phases of the first RF pulse and the fourth RF pulse.
The magnetic resonance imaging apparatus according to claim 3. The scan unit transmits the second RF pulse and the third RF pulse so that the absolute values of the flip angles are the same.
The magnetic resonance imaging apparatus according to claim 4. The scanning unit transmits a plurality of RF pulses including a 180 ° pulse as the second RF pulse, and transmits a plurality of RF pulses including the 180 ° pulse as the third RF pulse.
The magnetic resonance imaging apparatus according to claim 1. The scanning unit transmits the plurality of RF pulses to be transmitted as the second RF pulse and the third RF pulse, respectively, and have the same phase and the same absolute value of the flip angle. Send in reverse,
The magnetic resonance imaging apparatus according to claim 6. The scanning unit sequentially transmits an α ° pulse other than the 180 ° pulse and a 180 ° pulse as the plurality of RF pulses to be transmitted in each of the second RF pulse and the third RF pulse.
The magnetic resonance imaging apparatus according to claim 7. The scanning unit
In a plurality of gradient pulses transmitted as each of the first crusher gradient pulse and the second crusher gradient pulse,
The gradient pulse transmitted between the first RF pulse and the second RF pulse and the gradient pulse transmitted between the third RF pulse and the fourth RF pulse are set to the same first time integral value. And
The total time integral value of the gradient pulse transmitted between the plurality of RF pulses transmitted as the second RF pulse and the third RF pulse is doubled with respect to the first time integral value. So that the time integral value of 2
Transmitting each of the first crusher gradient pulse and the second crusher gradient pulse;
The magnetic resonance imaging apparatus according to claim 1. The scan unit transmits, as the preparation pulse, a speed encode gradient pulse that shifts the spin phase so that the phase of the spin varies depending on the spin speed of the subject.
The magnetic resonance imaging apparatus according to claim 1. The scan unit transmits the velocity encode gradient pulse so as to have opposite polarities in a time axis with respect to a central time point at which the velocity encode gradient pulse is transmitted.
The magnetic resonance imaging apparatus according to claim 10. An image generation unit that generates an image of the subject based on the imaging data;
The scanning unit
Obtaining a magnetic resonance signal generated as a result of performing the imaging sequence after the preparation sequence is implemented as a first preparation pulse sequence as first imaging data;
The same preparation pulse as that of the first preparation sequence except that the crusher gradient pulse and the velocity encode gradient pulse are not transmitted and the flip angles of the second RF pulse and the third RF pulse are different. After performing the second preparation pulse sequence to be transmitted as the preparation sequence, a magnetic resonance signal generated by performing the imaging sequence is acquired as second imaging data;
The image generation unit generates a first image based on the first imaging data, generates a second image based on the second imaging data, and then combines the first image and the second image. A difference image is generated as the image by performing difference processing.
The magnetic resonance imaging apparatus according to claim 10 or 11. The scanning unit transmits a killer gradient pulse that generates a gradient magnetic field that causes the transverse magnetization of the spin to disappear in the subject before transmitting the first RF pulse as the preparation pulse.
The magnetic resonance imaging apparatus according to claim 1. The scanning unit transmits each of the first RF pulse, the second RF pulse, the third RF pulse, and the fourth RF pulse as a rectangular pulse.
The magnetic resonance imaging apparatus according to claim 1. The scanning unit performs the preparation sequence during systole in the heartbeat motion of the subject, and performs the imaging sequence during diastole in the heartbeat motion.
The magnetic resonance imaging apparatus according to claim 1.

Images